New determination of the π− and νμ masses

Abstract The rest mass of the π − meson has been determined by measurements of the energies of π-mesonic X-rays with Ge(Li) detectors to be (139.549 ± 0.008) MeV (standard deviation). An upper limit of 0.6 MeV was deduced for the rest mass of the μ-neutrino (90% confidence).